CHAPTER XVI INSECTIVORA-----CHIROPTERA Order XL INSECTIVORA. THE Insectivora1 are an order of mammals to which it is \ quote Professor Huxley) "exceedingly difficult to give a definitio] They are, however, none of them large animals, and most of the are nocturnal in habit—two circumstances which may have hi something to do with their survival from past ages, as may ha also their modification to so many and diverse modes of lift for everything points to the antiquity of the group. They ai for instance, more or less plantigrade. The snout is general! long, and is often prolonged into a short proboscis.2 There ; a tendency for the teeth to be of a generalised type, an their number is often the typical mammalian forty-fou] Moreover, trltuberculate teeth, which are certainly an ancien form of tooth, are common; and indeed the Insectivora of tin southern regions of the globe, e,g. Centetidae, Solenodontidae, anc Chrysoehloridae, have the most prevalent trituberculism, a fact which is of importance in considering the age of the animal life of these regions of the world. The limbs are, as a rule, provided with five digits. The hemispheres of the brain are usually smooth, and do not extend over the cerebellum. The palate is often fenestrate as in the Marsupials, and as in that group the lower jaw is sometimes inflected. But the latter character also occurs in the Sea-lions and elsewhere. Clavicles are present, as a rule, but not in Potamogcde. 1 See especially Dobson, A Monograph of the Insectivora, London, 1886-90, 2 Even in the Otter-like Potamogale the upper jaw, though hroad and flat, projects considerably beyond the lower.